Variation of the posterior cerebral artery and its embryological explanation: a cadaveric study.

The posterior cerebral arteries are paired vessels that usually originate from the basilar artery at the level of the pontomesencephalic fissure and are joined by the posterior communicating artery to close the posterior portion of the Circle of Willis (circulus arteriosus cerebri). There is a considerable variation in the presence of the arterial segments of the circle of Willis. In the fetal type posterior cerebral artery there is an embryonic derivation of this vessel from the internal carotid artery. The irrigation of the posterior cerebral artery territory is thus completely dependent on the internal carotid artery. The term fetal-type posterior cerebral artery is used whether or not there is a communication with the basilar artery through a small pre-communicating segment (P1) of the posterior cerebral artery. This study deals with the variations of the posterior part of the circle of Willis, especially the origin of the posterior cerebral artery (PCA). The size of the posterior communicating artery (PComA) in comparison with the size of posterior cerebral artery is one of the principal differences between the fetal and adult forms of the circulus arteriosus cerebri. There are three configurations regarding posterior cerebral and posterior communicating arteries according to compare their diameters.